1. Field of the Invention
The present invention relates to a coil for use in a charged particle deflecting electromagnet used in, for example, a synchrotron radiation generating apparatus, and a method of manufacturing such a coil.
2. Description of the Related Art
FIG. 12 is a schematic plan view of a charged particle generating apparatus disclosed in, for example, Japanese Patent Laid-Open No 2300/1989. In the apparatus shown in FIG. 12, charged particles incident through an incident portion (not shown) and an acceleration portion (not shown) are deflected by two superconducting deflecting electromagnets 30 disposed in opposed relation and thereby move on an elliptical path 20.
FIG. 13A is a plan view of one example of a superconducting coil of the superconducting deflecting electromagnet 30 shown in FIG. 12, and FIG. 13B is a section taken along a line XIIIB--XIIIB of FIG. 13A.
Two superconducting coils 1, each of which is formed by winding a superconducting wire 2, are disposed in opposed relation at the upper and lower portion of the elliptical path 20. Each of the superconducting coils 1 is curved at a predetermined radius of curvature. The superconducting coil 1 has an inner diameter portion 1a located on the inner diameter side of the path 20, an outer diameter portion 1b located on the outer diameter side of the path 20 and curved in the same manner as the inner diameter portion 1a, and coil end portions 1c located between the inner and outer diameter portions 1a and 1b.
The thus-arranged superconducting coil 1 exhibits superconductivity when it is cooled to a temperature of, for example, -268.degree. C. Conduction of a current in the superconducting coil 1 exhibiting superconductivity produces a magnetic field having a high magnetic flux density of several teslas. The path 20 of the charged particles is bent in the manner shown in FIG. 12 by this generated magnetic field.
FIGS. 14A to 14C show another example of the conventional superconducting coil 1. This superconducting coil 1 has been described from page 2457 to page 2460 of IEEE TRANSACTIONS ON MAGNETICS, Vol. 1, Mag-24, No. 6, published in November 1985. FIG. 14A is a perspective view of the superconducting coil 1, FIG. 14B is a sectional view of the outer diameter portion 1b, taken along a line XIVB--XIVB of FIG. 14A, and FIG. 14C is a sectional view of the coil end portion 1c, taken along a line XIVC--XIVC of FIG. 14A.
In the superconducting coil 1 shown in FIG. 14, each of the coil end portions 1c is bent at a predetermined angle .theta. in a direction in which it is separated from the path 20 so as to allow the path 20 to be less affected by the magnetic field generated by the coil end portions 1c. This superconducting coil 1 is called the banana coil with bending ends. The superconducting coil 1 is disposed at the upper and lower portions of the path 20, as in the case of the coil shown in FIGS. 13A and 13B.
As shown in FIG. 14B, at the outer diameter portion 1b of the coil 1, N layers of the superconducting wire 2, from a first layer L1 to an Nth layer LN ,are laid on top of another in the horizontal direction with the first layer L1 being disposed on the innermost side. At the inner diameter portion 1a, layers of superconducting wire 2 are formed similarly with the exception that the first layer L1 is disposed on the right end. At each of the coil end portions 1c, the layers of the superconducting wire 2 are laid on top of another in the vertical direction with the first layer L1 being disposed on the lowermost side.
A conventional method of manufacturing the superconducting coils 1 shown in FIG. 14A will be described below with reference to FIG. 15.
First, the first layer L1 of the coil 1 is formed by winding the superconducting wire 2 a predetermined number of times in a left-handed fashion (starting from the outer diameter portion 1b, the coil end portion 1c, the inner diameter portion 1a and then the coil end portion 1c) and outwardly (starting from the uppermost portion as viewed in FIG. 14B). Subsequently, the second layer L2 is formed by winding the superconducting wire 2 along the first layer L1 in a left-handed fashion and inwardly. Thereafter, the superconducting wire 2 is wound similarly along the previous layer until the number of layers reaches the predetermined number N to manufacture the superconducting coil 1.
In the conventional superconducting coil of the above-described type, since the superconducting wire 2 must be wound in a curved fashion and three-dimensionally, a complicated winding device (not shown) is required, increasing production cost and hence the price of the coil. Furthermore, the superconducting wire 2 is sequentially wound outwardly to form the odd layers and inwardly to form the even layers. At that time, particularly when the even layers are formed, a gap may be generated between the adjacent superconducting wires 2 at the portion indicated by an arrow R in FIG. 15. With the gap between the adjacent superconducting wires 2, when a current is supplied to the superconducting coil 1, the wire 2 may be moved due to the electromagnetic force, generating quenching which leads to breakage of the superconducting state.